<!DOCTYPE html>
<html lang="en" xmlns:v-model="http://www.w3.org/1999/xhtml">
<head>
    <meta charset="UTF-8">
    <title>computed</title>
    <script src="https://cdn.jsdelivr.net/npm/vue@2.6.12"></script>

</head>
<body>
<div id="app">
    birthday:   <input type="text" v-model=birthday><br>
    name:       <input type="text" v-model=user.name><br>
    age         <input type="text" v-model=user.age>
</div>
<script type="text/javascript">
    var app = new Vue({
        el: "#app",
        data: {
            birthday: 1616566607104,
            user: {"name": "hello", "age": 1}
        },
        watch: {
            birthday(newValue, oldValue) {
                console.log(newValue);
                console.log(oldValue);
            }
        },
        user: {
            deep: true,
            handler(obj) {
                console.log(obj.name + "-" + obj.age);
            }
        }
    })
</script>
</body>
</html>